With the dangers associated with automobile travel, there is an ongoing need for enhanced automobile driver aides. One possible area of increased driver aides involves detection of objects behind a vehicle. As the vehicle approaches objects, moving forward or backing up, (e.g. other vehicles, pedestrians and obstacles) or as objects approach the vehicle a driver cannot always detect the object and take precautions necessary to avoid a collision with the object. To enhance the safety of trucks, for example, sensor systems or more simply “sensors” for detecting objects around a truck have been suggested. Such sensors typically include an acoustic, optical or infrared (IR) detector for detecting obstacles in the path of the vehicle moving forward or backwards. Prior art systems using acoustic and optical sensors have missing coverage areas close to the bumper and areas toward the far end of the coverage zone. The acoustic sensors have limited depth coverage and weather conditions degrade the performance of these sensors.
As is known in the art, there is an increasing trend to include radar systems in commercially available sensor products. For example, it is desirable to include radar systems in automobiles, trucks boats, airplanes and other vehicles. Such radar systems must be compact and relatively low cost. Furthermore, some applications have relatively difficult design parameters including restrictions on the physical size of the structure in addition to minimum operational performance requirements. Such competing design requirements (e.g. low cost, small size, high performance parameters) make the design of such radar systems relatively challenging. Among, the design challenges is the challenge to provide an antenna system which meets the design goals of being low cost, compact and high performance.
In such safety applications, it is necessary to provide a sensor capable of accurately and reliably detecting objects in the path of the vehicle. Radar is a suitable technology for implementing a sensor for use in vehicles such as automobiles and trucks. One type of radar suitable for this purpose is a Frequency Modulated Continuous Wave (FMCW) radar. In a typical FMCW radar, the frequency of the transmitted CW signal linearly increases from a first predetermined frequency to a second predetermined frequency. FMCW radar has the advantages of high sensitivity, relatively low transmitter power and good range resolution.
In automotive radar systems cost and size considerations are of considerable importance. Furthermore, in order to meet the performance requirements of automotive radar applications, (e.g. coverage area) an array antenna is required. Some antenna elements which have been proposed for use in antenna arrays manufactured for automotive radar applications include patch antenna elements, printed dipole antenna elements and cavity backed patch antenna elements. Each of these antenna elements has one or more limitations when used in an automotive radar application. Array antennas for automotive applications have only a limited amount of area for reasons of compactness and cost. Printed dipole antennas can operate in a high density circuit configuration, however, array antennas provided from printed dipole antenna elements sometimes give rise to “blind spots” in the antenna radiation pattern.
Sensors disposed on vehicles are consumer products that may affect the safety of the passengers, and the accuracy and reliability of these sensors are important. Aspects of the sensors which contribute to its accuracy and reliability include its susceptibility to noise and the overall precision with which received radio frequency (RF) signals are processed to detect objects within the field of view of the sensor. Susceptibility to noise for example can cause false detections or more deleteriously, cause an object to go undetected.
Further significant attributes of the sensors are related to its physical size and form factor. Preferably, the sensor is housed in a relatively small enclosure or housing mountable behind a surface of the vehicle. For accuracy and reliability, it is imperative that the transmit antenna and receive antenna and circuitry of the sensor are unaffected by attributes of the vehicle and that the sensors are mounted to the vehicle in a predictable alignment. In addition, when used as a back-up aid indicator, the sensor requires a coverage area which is compatible with the operation of backing up and parking a vehicle. Conventional FMCW radar systems have a minimum detection range which is unsuitable for back-up assistance. For example in some systems the minimum detection range is beyond 1.5 meters.
The use of radar systems to aid in parking, backing-up, changing lanes, and detecting objects on the side of the vehicle, requires in addition to a reliable low cost radar, a solution to a variety of geometric coverage problems matched to the particular application. Prior art systems using uncollimated signals provide beams having a typical aperture taper forming beams which spread such that the sides of the coverage area are not parallel and the width of the coverage area is relatively narrow. Thus the coverage of the prior art systems poorly matches a desired rectilinear back-up coverage area.
It would, therefore, be desirable to provide a sensor system which is capable of detecting the presence of objects behind a stationary or moving vehicle and further to detect the speed of these objects if the objects are moving. It would thus be desirable to alert the operator of the vehicle so the operator can safely maneuver the vehicle. It would be further desirable to provide a back-up aid system which is compact, which can operate in a high density circuit configuration, and which is relatively low cost. It would be still further desirable to provide a coverage zone including common parking and back-up coverage for reducing false detections. It would be further desirable, to provide an antenna which is low cost and can be flexibly mounted on a vehicle to provide a minimum detection range which is suitable for back-up and parking assistance.